Emergency workers pulled more than 100 survivors from the rubble of homes, schools and a hospital in an Oklahoma town hit by a powerful tornado, and officials lowered the death toll from the storm to 24, including nine children.

The search for survivors and the dead is almost complete, a fire chief said. Gary Bird said he was “98 per cent sure” there were no more survivors or bodies to recover under the rubble in Moore.

Mr Bird said every damaged home had been searched at least once, and that his goal was to conduct three searches of each location just to be sure.

“They pulled kids out from under cinder blocks without a scratch on them.” The Oklahoma state medical examiner’s office said 24 bodies had been recovered from the wreckage, down from the 51 they had reported earlier.

The earlier number likely reflected some double-counted deaths, said Amy Elliott, chief administrative officer for the medical examiner. “There was a lot of chaos,” she said.

The National Guard and firefighters from more than a dozen fire departments as well as rescuers from other states worked all night under bright spotlights trying to find survivors.

President Barack Obama declared a major disaster area in Oklahoma, ordering federal aid to supplement state and local efforts in Moore after the deadliest US tornado since 161 people were killed in Joplin, Missouri, two years ago.

“The people of Moore should know that their country will remain on the ground, there for them, beside them, as long as it takes,” Mr Obama said at the White House.

Glenn Lewis, the mayor of Moore, said the whole town looked like a debris field and there was a danger of electrocution and fire from downed power lines and broken natural gas lines. “It looks like we have lost our hospital. I drove by there a while ago and it’s pretty much destroyed,” Mr Lewis told NBC.

On Tuesday morning, a helicopter was circling overhead and thunder rumbled from a new storm as 35-year-old Moore resident Juan Dills and his family rummaged through the remains of what was once his mother’s home.

The foundation was laid bare, the roof ripped away and only one wall was still standing. They found a few family photo albums, but little else. “We are still in shock,” he said. “But we will come through. We’re from Oklahoma.”

The National Weather Service assigned the twister a preliminary ranking of EF4 on the Enhanced Fujita Scale, meaning the second most powerful category of tornado with winds up to 320 kph.

Authorities warned the town 16 minutes before the tornado touched down at 3:01 pm local time which is more than the average eight to 10 minutes of warning, said Keli Pirtle, a spokeswoman for the National Weather Service Storm Prediction Center.